The document discusses techniques for writing and balancing chemical equations, including representing molecules with chemical formulas, determining the number of atoms in different compounds, using conservation of mass to balance equations, and examples of balancing a variety of chemical reactions. It provides guidance on balancing a number of sample equations involving different elements and compounds.

1. Balancing Equations: Chemical and Nuclear

2. How molecules are symbolized Cl 2 2Cl 2Cl 2 Molecules may also have brackets to indicate numbers of atoms. E.g. Ca(OH) 2 Notice that the OH is a group The 2 refers to both H and O How many of each atom are in the following? a) NaOH b) Ca(OH) 2 c) 3Ca(OH) 2 Na = 1, O = 1, H = 1 Ca = 1, O = 2, H = 2 Ca = 3, O = 6, H = 6 O H O H Ca

3. Balancing equations: MgO The law of conservation of mass states that matter can neither be created or destroyed Thus, atoms are neither created or destroyed, only rearranged in a chemical reaction Thus, the number of a particular atom is the same on both sides of a chemical equation Example: Magnesium + Oxygen Mg + O 2  MgO However, this is not balanced Left: Mg = 1, O = 2 Right: Mg = 1, O = 1 O Mg O +  Mg O

4. Balance equations by “inspection” Hints: start with elements that occur in one compound on each side. Treat polyatomic ions that repeat as if they were a single entity. 5 2 3 3.5 2 7 4 6 2 2 2 2 6 3 C 2 H 6 + O 2  CO 2 + H 2 O a) P 4 + O 2  P 4 O 10 b) Li + H 2 O  H 2 + LiOH c) Bi(NO 3 ) 3 + K 2 S  Bi 2 S 3 + KNO 3 d) C 2 H 6 + O 2  CO 2 + H 2 O From Mg + O 2  MgO 2Mg + O 2  2MgO is correct Mg + ½O 2  MgO is incorrect Mg 2 + O 2  2MgO is incorrect 4Mg + 2 O 2  4MgO is incorrect

5. a) Mg + 2 HCl  MgCl 2 + H 2 b) 3 Ca + N 2  Ca 3 N 2 c) NH 4 NO 3  N 2 O + 2 H 2 O d) 2 BiCl 3 + 3 H 2 S  Bi 2 S 3 + 6 HCl e) 2 C 4 H 10 + 13 O 2  8 CO 2 + 10 H 2 O f) 6 O 2 + C 6 H 12 O 6  6 CO 2 + 6 H 2 O g) 3 NO 2 + H 2 O  2 HNO 3 + NO h) Cr 2 (SO 4 ) 3 + 6 NaOH  2 Cr(OH) 3 + 3 Na 2 SO 4 i) Al 4 C 3 + 12 H 2 O  3 CH 4 + 4 Al(OH) 3 skeleton(UNBALANCED) equations:

6. We have looked at several types of reactions without worrying about balancing However, all equations should be balanced Predict the products and balance these: (recall, metals above replace metals below, reactions with water yield metal hydroxides) Cu + Fe 2 (SO 4 ) 3 NR (no reaction) Zn + Li 2 CO 3 Cu + AlCl 3 Returning to reaction types Fe + CuSO 4  LiOH + H 2 Al 2 O 3 2 Ni + NaCl  Al + CuCl 2  Li + ZnCO 3  Li + H 2 O  Al + O 2  3 3 3 2 2 3 2 ½ 2 2 2 3 2 4 Cu Hg Ag Ca Mg Al Zn Fe Ni Sn Pb H Au Li Na K

7. a) 2 KNO 3  2 KNO 2 + O 2 b) 2 Pb(NO 3 ) 2  2 PbO + 4 NO 2 + O 2 c) P 4 + 6 I 2  4 PI 3 d) 3 MgO + 2 H 3 PO 4  Mg 3 (PO 4 ) 2 + 3 H 2 O e) Br 2 + 2 KI  I 2 + 2 KBr f) Ca(OH) 2 + 2 HNO 3  Ca(NO 3 ) 2 + 2 H 2 O g) Bi 2 O 3 + 3 H 2  2 Bi + 3 H 2 O h) 3 Fe + 2 O 2  Fe 3 O 4 i) 2 CaO + 5 C  2 CaC 2 + CO 2 Here are some more to balance: